The invention relates generally to a power conversion apparatus and, more specifically, to a universal combination VAC and VDC power conversion apparatus for portable electronic and electrically powered devices such as, for example, a personal computer.
Portable personal computers (PCs) and many other electronic devices are required to operate both from conventional alternating current (AC) mains and battery direct current (DC) power sources. Power conversion apparatus are known in the art which perform both the AC-DC and DC-DC conversions required to power such devices. An example of an apparatus which converts either AC or DC to DC power is disclosed in U.S. Pat. No. 3,769,571 to Wilkinson.
The apparatus disclosed in Wilkinson, as well as other similar power conversion apparatii known in the art, employs separate power conversion circuitry with respect to the AC to DC and the DC to DC conversions. For this reason, there exists a certain amount of duplicate circuitry within the converter. For example, each of the AC and the DC conversion circuits includes a switching circuit comprising two bipolar junction transistors (BJTs), each of which are shunted by a diode, and a transformer having two primary and one secondary windings. A third transformer, having a double primary winding, is also provided to invert the power prior to applying it to a DC load. In addition to having needlessly redundant circuitry, under certain power conditions, the efficiency of the multiple transformer arrangement is limited by its use of BJTs.
Accordingly, what is needed is an AC/DC power converter that overcomes the redundances previously required in the prior art, thereby reducing the size, weight and cost of the converter, and increasing its efficiency.